注意FLASH AS2中的null、undefined、NaN、""[1]

flash中null、undefined、nan、""这3个特殊的值是非常容易弄错的，不过大家可以从下面的语句中看出各自的区别：

var ddd0:string;

var ddd1:string = null;

var ddd2:string = undefined;

var ddd3:string = nan;

var ddd4:string = "";

trace("ddd0="+ddd0);

//output:undefined

trace("ddd1="+ddd1);

//output:null

trace("ddd2="+ddd2);

//output:undefined

trace("ddd3="+ddd3);

//output:undefined

trace("ddd4="+ddd4);

//output:

var ddd5:string = "233.2";

trace("ddd0="+number(ddd0));

//output:nan

trace("ddd1="+number(ddd1));

//output:nan

trace("ddd2="+number(ddd2));

//output:nan

trace("ddd3="+number(ddd3));

//output:nan

trace("ddd4="+number(ddd4));

//output:nan